Abstract: With the increasing requirement for the travelling comfort of high speed train, the reduction in interior noise becomes very important. Noise source identification is a prerequisite to the decrease in the interior noise. To study the effects of air conditioning system on the noise inside the high speed train, the comprehensive measurement of noise and vibration was made for different carriages of the high speed train. Analysis results of internal noise within different carriages in the running and static tests indicate that the air conditioning system has small effect on the interior noise and there are common significant characteristics of internal noise although the air conditioning systems within carriages are different. The main energy of internal noise is dominant in the low frequency range. The floor vibration excited by air conditioning system radiates the noise inside the carriage.